Sialolith crystals localized intraglandularly and in the Wharton’s duct of the human submandibular gland: an X-ray diffraction analysis

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Abstract

The exact cause of the formation of sialoliths is unknown. Detailed knowledge of pathogenesis of sialolithiasis and composition of sialoliths is necessary to define new therapeutic procedures. The crystalline components of 23 sialoliths of human submandibular gland were investigated by X-ray powder diffraction analysis. All of the sialoliths localized in the ducts in the submandibular gland consisted of hydroxylapatite. However, in the sialoliths in the Wharton’s duct, hydroxylapatite as well as whitlockite and brushite could be found in all except one case. Whitlockite was observed more often in the nucleus of the sialoliths and it was a common co-phase along with hydroxylapatite. The nucleus in one sialolith consisted of brushite and the cortex showed a co-phase of hydroxylapatite and brushite. The occurrence of whitlockite in the sialoliths in Wharton’s duct may be due to a higher concentration of calcium and phosphate in saliva in this duct.

Introduction

The disturbance in salivary secretion and the change in the composition of saliva, which was called dyschylia by Seifert,1 leads to an increase in salivary viscosity and to a slime obstruction in the terminal ducts of the gland. The disturbance in salivary secretion and increased formation of microliths in ducts support the ascent of bacteria and cause focal obstructive atrophy of the gland parenchyma. This is associated with proliferation of bacteria and inflammatory reactions in salivary gland tissue.2 The development of sialoliths is a multifactorial event, in which disturbances in secretion, microliths and bacteria may play the major role.3

The most important phases of lithogenesis are the enrichment of organic substances, in particular of glycoproteins with high calcium affinity, and mineralization of the organic matrix in the duct system. Mineralization is supported by accumulation of calcium and an increase in pH, which then decreases the solubility of the calcium phosphates in saliva.4 Sialoliths consist of heterogeneous mixture of different phosphates of calcium and apatite is the most frequent component present throughout the sialoliths.5 There are individual differences in the structure and mineralization of sialoliths. The nucleus of the sialoliths is mostly inorganic, predominantly made up of calcium phosphate and calcium carbonate in the apatite structure. Around this amorphous nucleus, laminar layers of organic and inorganic substances accumulate and their content varies within a single sialolith. The organic material is predominantly concentrated in the outer shell of the sialoliths and their components are mostly glycoproteins, mucopolysaccharides, lipids and cell detritus.6

For better understanding of the pathogenesis of sialolithiasis, the exact knowledge of the composition of sialoliths is necessary. The aim of the present study was to analyse the mineral composition of submandibular sialoliths in the nucleus and cortex of each sialolith and to ascertain whether there are differences in mineral composition between sialoliths localized intraglandularly or in Wharton’s duct.

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Materials and methods

Twenty-three sialoliths removed from submandibular glands were used for the present study. These samples were collected from patients with chronic obstructive sialadenitis (9 females and 14 males; mean age 45.4; range 23–76). Eleven of the extirpated sialoliths were localized in the ducts in the submandibular gland and 12 were localized in Wharton’s duct. The sialoliths had been removed within the last 3 years and were stored after rinsing with distilled water and air drying. All sialoliths had

Results

In all of the examined sialoliths, a nucleus could be found which has a comparatively softer consistence than the outside parts of the sialoliths. There was no relation between the size of the sialoliths and the size of the nuclei.

The main crystal constituent in all the examined samples was hydroxylapatite in both inner and outer parts of sialoliths. All sialoliths localized in the ducts in the submandibular gland consisted of hydroxylapatite. However, in those in the Wharton’s duct,

Discussion

Sialolithiasis is the most common disease of the salivary glands in middle-aged patients. It is estimated that sialolithiasis affects 1.2% of the population.7 More than 90% of the sialoliths occur in the submandibular gland.8 The great majority of these sialoliths is localized in the Wharton’s duct. The ratio of sialoliths localized intraglandularly to those in Wharton’s duct is 3:7.7 In comparison to the other salivary glands, the submandibular gland is rich in viscous secretion of high

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